This invention relates to a method of applying a fused silica coating to a substrate of refractory non-metallic material and, more particularly, relates to a method of applying such a coating by arc plasma spraying.
For certain high temperature applications, e.g., an arc chute for an electric circuit breaker, fused silica is a nearly ideal material due to its exceptionally high resistance to thermal shock, its good electrical insulating properties, even when hot, and its ability to withstand exposure to a high current arc with little erosion and with little evolution of gases. Efforts have been made to apply the fused silica coating to a substrate by an arc plasma spraying process, but those prior efforts of which we are aware have not been very successful because the particles impinging against the substrate either have not formed a coating or have not adhered sufficiently firmly to the substrate. In addition, these efforts have encountered spraying difficulties, such as the formation of fibers instead of molten droplets, which fibers have clogged the plasma spray gun.